Effect of asymptomatic transmission and emergence time on multi-strain viral disease severity
Abstract
Background
In a viral epidemic, the emergence of a novel strain with increased transmissibility (larger value of basic reproduction number R 0 ) sparks the fear that the increase in transmissibility is likely to lead to an increase in disease severity. It is required to investigate if a new, more contagious strain will be necessarily dominant in the population and resulting in more disease severity.
Methods
The impact of the asymptomatic transmission and the emergence time of a more transmissible variant of a multi-strain viral disease on the disease prevalence, disease severity, and the dominant variant in an epidemic was investigated by a proposed 2-strain epidemic model, called 2-SEICARD model, that is an extension of the SEIRD model.
Results
The simulation results showed that considering only R 0 , is insufficient to predict the outcome of a new, more contagious strain in the population. A more transmissible strain with a high fraction of asymptomatic cases can substantially reduce the mortality rate. If the emergence time of the new strain is closer to the start of the epidemic, the new, more contagious variant has more chance to win the viral competition and be the dominant strain; otherwise, despite being more contagious, it cannot dominate previous strains.
Conclusions
Three factors of R 0 , the fraction of asymptomatic transmission, and the emergence time of the new strain are required to correctly determine the prevalence, disease severity, and the winner of the viral competition.
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